Hi,
I tried to use both ftp_put() and ftp_nb_put() adding the
variable $start = date("Y:m:d h:i:s"); at the begin of the script and the variable $end = date("Y:m:d h:i:s"); at its end, after the file upload function.
With the gprs connection I'm now using and trying to upload a .jpg file of 67,5 kb the time difference between $start and $end was 40 seconds in both cases, so I can suppose that there is no difference between these upload function.
The difference comes if you put anything inside the while ($ftp_upload == FTP_MOREDATA) loop.
I hope this note can help.
Regards